The present invention relates to electronically commutated electric machines, in particular methods for the sensor-free position detection of an armature of an electric machine.
Information on the instantaneous armature position is required for electronic commutation of brushless electric machines. Electronic commutation is carried out with the aid of the armature position by virtue of phase voltages being applied to the electric machine depending on the armature position or, in the case of operation in the generator mode, being tapped off at said electric machine.
Various methods for ascertaining the armature position are known. In the case of one group of electric machines, the armature position is detected by an integrated or separate position sensor and made available to the control unit which performs the electronic commutation. In the case of another group of electric machines, the armature position is ascertained without the use of sensors from the motor voltages and/or motor currents.
A known method for sensor-free position detection is the so-called back-emf method, in which an armature position is derived from a profile of the induced voltage in a winding phase of the electric machine. Since it is necessary to switch the corresponding phase connections to the deenergized state in order to measure the induced voltage, restrictions are placed on the choice of suitable energization pattern for the electronic commutation for the use of the back-emf method.
Furthermore, armature position determination with the aid of the back-emf method is generally possible precisely in the case of those electric machines in which the induced voltage describes a sinusoidal profile and the phase voltages are not supplied via an inverter since a phase connection cannot be switched to the deenergized state there. A permanent voltage input (without blanking interval) which is advantageous, for example, for the noise response is not possible with a back-emf method. The quality of known methods for the sensor-free operation of sinusoidal machines such as, for example, in the case of sensor-free, field-oriented regulation decreases the more the profile of the induced voltage deviates from a sinusoidal profile.